The invention relates to an apparatus for inverting and returning sheets from a printer for large-sized paper, said apparatus comprising an inlet area where the sheet is received from the printer, and an outlet area where said sheet is returned to the printer, a front edge of the sheets remaining in front during the receiving, inverting and returning movement of said sheets.
Various printers for large-sized paper are known, such as for instance the HP Designjet 1050C/1055CM. Such printers are primarily used for simplex printing, viz. printing on one side of the paper, and they are often used for the production of samples of for instance posters before the final printing is initiated. The paper is available in form of separate sheets fed manually into the printer from the front side of said printer, or it is available in form of rolls fed into the printer through a suitable inlet and cut off therein in the desired length, said length being variable according to desire. After the printing procedure, the paper usually falls into a tray or basket arranged below the printer, said tray or basket being secured to the support of the printer.
Sometimes duplex printing is required, viz. printing on both sides of the paper, and then it is necessary to invert the paper, which, of course, can be carried out manually, but various possibilities of automating said inverting procedure apply as well. Some printers allowing such a duplex printing comprise two printer sections for initiating the printing on each side of the paper. Other printers comprise a built-in sheet inverter integrated in the inlet area of the printer with the result that it obstructs the passage of the sheet when said sheet is to be returned to the tray.
The object of the invention is to provide an apparatus for inverting and returning sheets to a printer, where said apparatus is mounted independent of the printer and accordingly does not obstruct the usual operation of the printer during the printing on only one side, and where said apparatus furthermore can be mounted on an existing printer, such as a printer of the type described above, in a relatively easy manner.
The apparatus according to the invention comprises a frame mountable on the support of the printer, and a guiding slit in the inlet area, said guiding slit being defined by a downward surface on an upper guiding wall and an upward surface on a lower guiding wall, where said upward surface having a downwardly curving profile extends from the inlet area to a clamping slit between a first pair of roller means, whereby the lower guiding wall is tiltable and adapted to be moved about a substantially horizontal axis from a sheet-supporting and -forming position in which the guiding slit is formed and into a downwardly extending sheet-releasing position, where in use the outlet area is placed over and adjacent the inlet area, and where the frame carries a second pair of roller means adapted to receive the sheet from the first pair of roller means and to guide the sheet through the outlet area and back to the printer.
As a result the inverting of a sheet can be carried out completely outside the printer, and the resetting of the printer to an inverting of the sheet or to an ordinary use can be controlled merely by moving the lower guiding wall between its two operational positions while it is simultaneously possible to move the entire sheet out of the printer before it is returned to the printer again. The latter is in particular achieved by the front edge of a sheet to be inverted being advanced to and retained in the clamping slit between the first pair of roller means, whereafter the lower guiding wall is moved out of its sheet-supporting position and allows said sheet to be moved outwards into an increasing, downward loop in the area between the outlet of the printer and the first pair of roller means until the rear end of said sheet falls out and downwards into the area below the printer where a basket is preferably provided. Subsequently, the sheet is pulled upwards and fed into the printer again by an activation of the roller means.
According to the invention it is particularly advantageous when the apparatus comprises an idler roll adapted to abut the top side of a sheet between the inlet area and the first pair of roller means after the front edge of the sheet has been gripped by the first pair of roller means and the lower guiding wall has been tilted downwards into the downwardly extending position, said idler roll being supported by the sheet and following said sheet in its downwardly curving free path as said sheet leaves the printer. As a result it is ensured that the sheet does not form folds substantially longitudinal to said sheet when seen in the advancing direction thereof, especially due to various degrees of moisture applied during the printing when seen in the transverse direction of said sheet.
According to the invention the idler roll may be suspended in a spring means ensuring that the idler roll subjects the sheet to a force weaker than the force originating from the weight of said idler roll, said spring means being connected to a driving means for retracting the idler roll into its uppermost starting position when the rear end of the sheet has passed the inlet area and has fallen down. In this manner it is avoided that the effect of the idler roll on the paper is restricted, and that said idler roll is easily returned to its starting position.
The two pairs of roller means may according to the invention particularly advantageously comprise a common roller and be driven by means of the roller means of the first pair of roller means co-acting therewith, whereby a simple control of the operation of the roller means is obtained.
According to the invention the apparatus comprises advantageously a first sensor for detecting the arrival of the front edge of a sheet immediately before said edge reaches the clamping slit between the first pair of roller means, and for activating said first pair of roller means so as to grip and advance said edge a short distance. As a result a high security is obtained that the first pair of roller means achieves a good grip in the front end of the sheet before the lower guiding wall is moved out of the sheet-supporting position.
Correspondingly the apparatus may according to the invention comprise a second sensor for detecting that the rear end of the sheet has left the printer. In this manner the returning of the above roller to its uppermost position and the further returning of the sheet to the printer are controlled in a simple manner.
Moreover, a measuring device may according to the invention be provided in connection with the second pair of roller means for registering the length of the sheet. As a result it is possible to efficiently monitor the operation of the apparatus despite a varying resistance relative to the advancing of various lengths of sheets and weights of paper etc. in such a manner that it is always positively known when the front end of the sheet has reached a specific predetermined location in the printer during the advancing and when said advancing by means of the roller means is to be stopped.
Furthermore, the driving roller means may according to the invention be provided with overrunning clutches so as to ensure that the sheet can be freely pulled forwards in the advancing direction when the advancing device of the printer starts to advance the inverted sheet. In this manner it is avoided that the sheet is destroyed due to the effect of various advancing speeds.
Moreover a redirecting member may according to the invention be provided at the guiding slit, said redirecting member being adapted to direct the front edge of a sheet downwards and into the guiding slit at the arrival from the printer, whereby the paper is reliably fed into said guiding slit. The latter is of particular importance when the paper originates from a roll and accordingly has a tendency to bend upwards in a direction away from the guiding slit.
The redirecting member may according to the invention particularly advantageously comprise a Z-shaped sectional guide freely pivotally journalled about a horizontal axis above the outlet area, where the body of said Z-shaped sectional guide in the rest position extends obliquely downwards and abuts by its lower end the edge of the upper guiding wall of the guiding slit adjacent the printer, and together with this guide rail it forms an acute angle facing the outlet area while the lower web of the sectional guide projects obliquely upwards from the guiding wall towards the printer. According to its size the upper web ensures a good balancing of the sectional guide.
The frame may according to the invention be tiltably and detachably mounted on the support of the printer in such a manner that an easy access applies to the side facing the printer.
Finally, a further guide may according to the invention be provided between the two pairs of roller means and the second pair of roller means and the outlet area, respectively, in such a manner that an efficient guiding of the sheet during the advancing thereof is obtained.